1. Field of the Invention
The present invention relates to a method for retaining or increasing the content of .gamma.-aminobutyric acid having an antihypertensive function in the green leaves of grass plants.
2. Description of the Related Art
Green leaves of grass plants, such as the young leaves of barley, wheat, rye, oats, adlay, Italian ryegrass, rice, and the like, are rich in vitamins, minerals, dietary fiber, and so on. They have therefore received attention for their usability as materials for health food products that provide the effects of adsorbing harmful substances, improving the intestinal environment, suppressing absorption of cholesterol, preventing the postprandial sudden rise in blood sugar, activating superoxide dismutase (SOD), and the like. When such young leaves, for example, are used as a material for health foods, they are presented in various forms. For instance, the young leaves of barley are directly dried and powdered to obtain leaf powder (Japanese Patent No. 2544302), or processed into the forms of juice, extract, and powder of such juice and extract (Japanese Laid-Open Patent Publication No. 11-75791). In either case, products having useful ingredients such as dietary fiber and vitamins retained therein in a larger amount are more preferable.
Green grass leaves contain enzymes such as chlorophyllase, peroxidase, and polyphenol oxidase that cause degeneration such as the fading of the vivid green color of green leaves. In order to prevent such degeneration, green leaves are generally subjected to hydrothermal treatment (i.e., blanching). During this treatment, ingredients naturally contained in green leaves, such as vitamins, minerals, and chlorophyll, tend to be lost.